ac ac ac re re ac re re re re

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int a, b, c;
    cin >> a >> b >> c;
    if (a % c != 0 || b % c != 0)
    {
        cout << "-1";
    }
    else
    {
        long long ac = a / c, bc = b / c;
        cout << ac * bc;
    }
    return 0;
}

看了题解